This invention relates in general to load positioning systems and, in particular, to a stabilizing system for maintaining the position of a suspended load in alignment with the plane upon which the load is to be placed. While the invention may be used for any application wherein it is desired or necessary to maintain vertical movement of a suspended load perpendicular to the surface upon which the load is to be placed, for convenience of illustration a preferred embodiment will be described with reference to its use with a hatch cover crane for positioning a hatch cover on a hatch coaming or cargo hold opening.
In seagoing vessels such as cargo-carrying ships, spaced openings are provided along the top of the deck, referred to as cargo hold openings or hatches. Various types of cargo, or bulk materials, are conveyed through these hatches into the ship's hold for transporting overseas. In order to protect the cargo contained within the ship's hold from the weather and elements encountered during a voyage, and to insure the ship's seaworthiness during heavy weather, these cargo hold openings are provided with a close-fitted covering, which is commonly referred to as a hatch cover. These hatch covers are made of a strong, heavy and durable metal adapted to fit closely about and cover the hatch coaming--a raised frame portion which extends upwardly around the hatch way to prevent water from running across the ship's deck into the ship's hold.
The use of heavy metal for the hatch cover results in the hatch cover being extremely bulky and heavy in order to withstand high wind forces, and the force of water which may pass over the ship's deck during heavy weather. In order to remove these hatch covers on some ships, a hatch cover crane is carried on the ship's deck. The hatch cover crane is movable along the length of the deck into a position directly over each of the hatch covers to remove and replace the hatch cover from the coamings.
In operation, the hatch cover crane is usually supported upon a pair of parallel tracks or rails which are positioned with one rail on each side of the hatches permitting the crane to straddle the hatch covers. The hatch cover crane is movable into a position directly over a hatch cover, and by proper positioning of the crane along these rails, hooks or other suitable engaging devices are aligned for attachment to the hatch cover. The crane lifting mechanism is then actuated to raise and remove the cover from the coaming, providing access to the ship's hold, or to lower the raised cover for closing the hatch.
During loading and unloading of the ship's hold, as is known, the ship may list to either side or fore and aft. Also, when attempting to replace the hatch cover on the coamings, a wind force may be encountered such that the raised cover shifts or oscillates making it difficult or impossible to maintain the hatch cover parallel to the ship's coamings. Since the fit between the hatch cover and the hatch coamings is necessarily generally with somewhat close tolerances, the position of the hatch cover and the hatch coaming has to be aligned in a parallel relationship to facilitate removal and replacement of the hatch cover. While movement of the crane along the pair of rails can compensate for some misalignment when replacing the hatch cover, such as due to fore and aft list, provision must be made to compensate for list to either side and lateral wind loading.
The hatch cover crane and hatch cover stabilizing system, to be described in detail hereinafter, provides a mechanism for removing the hatch cover from a hatch opening, and for replacing the removed cover on the opening whether or not the ship is listed to either side, fore or aft, or encounters a lateral wind load on the hatch cover. In addition, the stabilizing system provides a damping system for controlling oscillatory motion, such as occurs when the crane accelerates or decelerates while carrying a suspended cover.
The hatch cover crane includes a pair of hoist spreaders each carrying a hook for engaging the hatch covers. The hoist spreaders are positioned in spaced parallel relationship by a pair of struts and are raised and lowered through a plurality of hoist cables. A stabilizer cable system is secured to the hoist spreaders, and functions to provide a countering force to the lateral loading applied to the suspended hatch cover whether due to the ship listing to either side or wind loading, and dampens oscillatory movement. In this manner, the lateral force applied to the hatch cover will be balanced by the stabilizing system, and the cover may be raised and lowered perpendicular to the plane of the ship's deck. The hatch cover suspended from the hatch crane will thereby be in proper registry with the hatch coamings, regardless of the angles of list or trim of the vessel, or the wind forces encountered during a loading or unloading operation.